1. Field of the Invention
Devices consistent with the present invention relate generally to a liquid crystal display devices, and more particularly to liquid crystal display devices which are capable of uniformly maintaining brightness by uniformly distributing a temperature formed by heat emitted in a body of the liquid crystal display device.
2. Description of the Prior Art
Recently, related art flat-panel display devices such as a liquid crystal display (LCD) device, a plasma display panel (PDP), and an organic light emitting diode (OLED) have been mainly developed instead of the conventional cathode ray tube (CRT) display devices.
Among them, the related art LCD device includes a thin-film transistor substrate, a color-filter substrate, and a liquid crystal panel having liquid crystal injected between the thin-film transistor substrate and the color-filter substrate.
Since the related art LCD device is a non-emissive device, a backlight unit is positioned at a rear portion of the thin-film transistor substrate so as to provide light to the LCD device. In addition, a transmittance of light irradiated from the backlight unit is adjusted according to an alignment state of the liquid crystal.
In addition, the related art LCD device further includes a chassis accommodating the liquid crystal panel and the backlight unit therein.
Light sources used in the backlight unit include a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a flat fluorescent lamp (FFL), and a light emitting diode (LED). Recently, since the LED has high color reproducibility, a long life span, and low power consumption among the light sources, the LED has been mainly used as a light source of the backlight unit.
The backlight unit may be classified into an edge-light type backlight unit and a top-down type backlight unit according to a position of the LED. The edge-light type backlight unit has a structure in which a light source is installed in a side surface of a light guide plate, and is mainly employed for a small-size LCD device such as a laptop computer, or a desktop computer. Such an edge-light type backlight unit has superior uniformity of light and superior endurance, and is suitable for a slim LCD device.
As a size of the LCD devices has increased, the top-down type backlight unit has been actively developed. The top-down type backlight unit has a structure in which at least one light source is arranged at a rear portion of the liquid crystal panel so as to irradiate light onto the entire surface of the liquid crystal panel.
The related art LCD devices have a structure in which a heat emitting member is provided at a rear portion of a substrate having light sources arranged thereon so as to discharge heat, which is generated from the light sources, to the rear portion of the heat emitting member. However, the temperature distribution in the vicinity of the light sources is such that a temperature in an inner upper portion of the LCD device is higher than a temperature in an inner lower portion of the LCD device, and a temperature in a center portion of the LCD device is remarkably higher than a temperature in both sides of the LCD device due to a convection current phenomenon.
The irregular temperature distribution affects an optical power of the light source. Especially, the optical power is excessively changed according to temperatures in the case of a light source emitting red color light. Accordingly, when a user views an image projected on the liquid crystal panel, the image seems to be irregular and stained.
In addition, a life span of the LED is affected by the temperature. In other words, an LED under high temperature has a shorter life span compared with a life span of a light emitting diode under low temperature. Accordingly, if the temperature difference in the inside of the LCD device is excessive, dead light emitting diodes may exist together with active light emitting diodes in one LCD device.